Most of the mods were capacitor replacement. Between his thick accent and the fact that I'm not an electical engineer I didn't learn a lot. He too said the Chinese tubes were junk. I've gone online and seen that there are a few shops in the states that can do some substantial upgrades to the Shanling and turn it into a very nice sounding player. But the price of the upgrades can sometimes be $1,500. That's more than I have in to this player as is.